1. Field of the Invention
This invention relates to a plasma display panel which relies upon a gas discharge for the display of an image and a process for producing such a panel.
2. Description of the Prior Art
FIGS. 1 and 2 of the accompanying drawings are top plan and sectional views, respectively, showing the arrangement, prior to assembly, of various parts of a known plasma display panel as disclosed, for example, in the Japanese patent application laid open under No. 150523/1980. The panel includes a back panel member 1 provided with cathodes, not shown, as discharge electrodes, and formed therethrough with a gas port 2. It also includes a front panel member 3 provided with anodes 4 as discharge electrodes which are isolated from one another by insulating partitions 5. The back panel member 1 carries a deposit of glass 6 which is used for joining the back and front panel members 1 and 3 along the edges thereof and forming a seal therebetween. A glass tube 7 is connected to the port 2 for introducing a gas into the plasma display panel as assembled, or removing it therefrom. A deposit of glass 8 is used for joining the glass tube 7 to the back panel member 1 and forming a seal between the port 2 and the adjacent end of the tube 7. The back and front panel members 1 and 3 and the glass 6 define a vacuum enclosure when the panel is assembled.
The deposits of glass 6 and 8 are melted by heating for joining the back and front panel members 1 and 3, and the back panel member 1 and the glass tube 7, respectively, in a sealed way, as shown in FIG. 3. The inside of the assembly is filled with a gas 9, and the glass tube 7 is melted and cut by e.g. a gas burner to form a closure 10, whereby the gas 9 is isolated from the atmosphere, as shown in FIG. 4.
Referring in further detail to the process as hereinabove described, the deposits of glass 6 and 8 as shown in FIG. 2 are first softened by heating. The softened glass 6 is deformed by the weight of the back panel member 1 or an external force applied to it until the back panel member 1 contacts the insulating partitions 5 and has a smaller distance from the front panel member 3. The glass 6, as well as the glass 8, is cooled to ambient temperature, and thereby solidified, whereupon a sealed assembly is formed, as shown in FIG. 3. Then, the inside space of the assembly as defined between the back and front panel members 1 and 3 is evacuated through the glass tube 7 and the gas 9 is introduced into the space through the tube 7. Finally, the closure 10 is formed on the glass tube 7, whereupon the plasma display panel is assembled, as shown in FIG. 4.
The conventional panel as hereinabove described, however, has a part of the glass tube 7 remaining on the back panel member 1, as shown in FIG. 4. The length of the remaining part of the glass tube 7 adds to the thickness of the panel and renders it impossible to make any panel having a smaller overall thickness. The glass tube 7 projecting from the back panel member 1 not only calls for special care to be taken to protect the glass tube 7 against any shock, but also makes the panel as a whole so bulky that inconveniences may be encountered in the handling, packing or transportation of the panel which is being assembled, or has been assembled.
FIG. 5 illustrates a process proposed for improving the problems as hereinabove pointed out. This process does not employ any glass tube as shown at 7 in FIGS. 1 to 4. According to this process, a back panel member 1 and a front panel member 3 are joined to each other by glass 6 forming a seal therebetween, and a ring 11 of low-melting glass is deposited on the outer surface of the back panel member 1 coaxially with a gas port 2. A closing plate 13 carrying a deposit of low-melting glass 12 is placed on the ring 11, so that the glass 12 may lie between the ring 11 and the plate 13, and the plate 13 is held against the ring 11 by a clip, or like jig 14. The glass 12 has pores 15 which maintain fluid communication between the inside and outside of a panel defined by the back and front panel members 1 and 3. The panel is placed in a vacuum tank and is subjected to evacuation and degassing until a vacuum degree of 10.sup.-7 torr is reached in the inside of the panel. Then, a discharge gas is introduced into the tank to fill the inside of the panel. Finally, the whole assembly is heated, so that the low-melting glass 11 and 12 may be softened and fused together to form a seal closing the port 2.
The closing plate 13, however, remains projecting from the back panel member 1 and its thickness adds to the overall thickness of the plasma display panel. Therefore, the proposed process is not a satisfactory solution to the problems as hereinbefore pointed out, including the inconveniences in handling, and the bulkiness of the panel. Accordingly, it has been proposed that the closing plate 13 be fitted in a recess formed in the outer surface of the back panel member 1 along the edge of the port 2. The maintenance of satisfactory strength in the recessed portion of the back panel member 1, however, calls for an increase in thickness of the back panel member 1. This increase is contrary to the desire to reduce the thickness of the panel as a whole and brings about an increase in weight thereof.